1. Field of the Invention
The present invention relates to an LED control circuit, and more particularly to an LED control circuit with auto ON/OFF function.
2. Description of Related Art
A light-emitting diode (LED) device has advantages of high brightness and low power dissipation. The LEDs can be applied for illumination and decoration. For example, an LED string can have multiple LED devices connected in series. Such LED string can be used as a decoration light string during festive occasions.
The LED device is an electric device that is activated by a forward bias voltage. For example, the LED string can be activated by a PWM signal. The PWM signal comprises multiple high potentials and low potentials changed alternately. The LED string is activated in the high potentials but inactivated in the low potentials. Therefore, the LED string flashes.
However, the flashing performance of the LED string is poor because the LED string is only activated in the high potentials of the PWM signal. The LED string is not actuated in the low potentials. Hence, the use of the PWM signal is inefficient.
In additional, the LED string is usually connected to a power source via a switch. In the daytime, the LED string does not need to be activated. A user can press the switch to turn OFF the LED string. At night, the user has to press the button again to turn ON the LED string. The user may press the button several times in a day, especially in a shopping area where variations in flow of customers need to be taken into account. Hence, it is inconvenient for the user to manually turn ON/OFF the LED string.